This invention pertains to novel microparticulate material, the particles of which are sometimes referred to as microcapsules and to a method for making such material. More specifically, this invention pertains to microcapsular material comprising the reaction product of a salt form of a Lewis acid in an aqueous solution and the salt form of a Lewis base in a non-aqueous solution, wherein said microparticles may act as a carrier for diffusable reactants, such as chemicals and pharmaceuticals in order to serve as sustained or controlled release "microencapsulated" delivery forms.
Microencapsulation is a technique of enclosing core materials within a polymeric membrane to produce microparticles. The encapsulated material may be released over a period of time by diffusion or immediately by crushing or by digesting the shell-like wall of the microparticle. These types of microparticles are used extensively in the dye, and the food and cosmetic industries.
In the pharmaceutical industry, considerable interest has been generated by the use of microparticles as sustained release drug delivery formulations. However, many microparticle formulations are of limited utility because of their relatively large particle size. A particle size of greater than that of an erythrocyte (about 7 microns) is not suitable to be injected intraveneously.
Further problems with known prior art microparticulate material arise from the fact that generally such material tends to agglomerate, thus deleteriously affecting certain important properties of the materials such as dispersability. Additionally, microparticulate material which is of suitable size for injection may also be captured by the reticulo-endothelial system, which can have deleterious effects on blood clearance of the microparticle shell material and tissue distribution of the encapsulated core material.
A specific type of microparticulate material and a method of making such a material is disclosed in U.S. Pat. No. 3,959,457 (of common inventorship and assignment herewith). This material is comprised of the reaction product produced at the inter-phase boundary of a finely dispersed emulsion, comprising:
(I) a water immiscible solution of an organic polyfunctional Lewis base in a low boiling point, slightly polar, organic solvent; and
(II) an aqueous solution of a partially hydrophilic, partially lipophilic, polyfunctional Lewis acid.
Microparticles of this type comprise a multiplicity of closed structures formed of lattice-like high molecular weight salt molecules of the Lewis acid and Lewis base, through which an encapsulated core material diffuses. The rate of diffusion is controlled by both the particle or molecular size of the encapsulated compound and by the openness of the lattice or network of molecules comprising the particle walls. The degree of openness of the lattice is controlled by the spacing of reactive sites on the high molecular weight polyfunctional Lewis acids and by the thickness of the particle walls.